Just because I saw this piece on Ebay, and this guy didn't share this here. (http://tiny.cc/mar67w)
I think that reprap world is sharing spirit so I hacked this! ;)
Just be free to print this piece! ;)
-1 x 0608 bearing
-2 x m5 bolts
-2 x M5 screws
-1x M8 bolt
-1 x M8 screw
-2x M8 washers
This piece is just held by the tension of the belt.
You can also cut the 2 rods if they are too long for your belt.
Edit: Add M4 and 628ZZ STL.